1. Field of the Invention
The present invention relates to an improved electrical cable transition and method for an underground well and, more particularly, to a simplified, low cost, transition and method for such a cable. The transition includes NRTL approved primary and secondary seals and a cable connection between the seals along with a drain or vent for venting combustible or flammable well fluids to the atmosphere in case the primary seal leaks.
2. Description of the Related Art
In underground wells such as oil wells, electrical power is furnished to submersible pumps and other downhole equipment through insulated electrical conductors that extend through conduit in the well casing. In order to connect the downhole equipment to a power source outside the well, these conductors must penetrate a wellhead barrier that is sealed to a top opening of the casing. The configuration of cables and seals in the wellhead is called a "penetrator," the purpose for which is to provide a transition zone where the cable penetrates the wellhead barrier, and gas and other fluids are prevented from leaking both into and out of the well.
Because the downhole equipment must be connected to an above-ground power source, a splice or other connection must be formed between cable connected to the power source and cable extending from the downhole equipment. This splice has been formed below the wellhead barrier in the past, which isolates the splice from the area around the outside of the wellhead barrier which is classified as a hazardous location.
Such hazardous locations are referred to as being "classified" because they are defined or classified by industry standards such those promulgated by the American Petroleum Institute. The equipment and facilities for such classified locations must be in compliance with the Occupational Safety and Health Act ("OSHA") Section 1910, Subpart S, for locations where hazardous concentrations of gases or vapors are present because of leakage.
A penetrator which has gained acceptance in the oil industry is shown and described in U.S. Pat. No. 5,829,882, which has the same inventor as the inventions described below. This penetrator solved the problem of providing a sealed arrangement for supplying electrical power to a sealed wellhead over a petroleum producing well bore in an area classified as hazardous, where explosions or fires may occur due to gases and other substances associated with the production of petroleum products being ignited by electric arcs. The penetrator in U.S. Pat. No. 5,289,882, included a rigid conduit with a splice fitting formed below the wellhead barrier, for connecting the downhole electrical conductors of a wellbore power cable with electrical conductors extending from a power source on the surface. A rigid conduit was provided for containing the conductors in the well, as they extended from the splice fitting to a rigid conduit outside the wellhead barrier which had a breather vent to inhibit the passage of fluids from the downhole electrical conductor to the power source electrical conductor. An arrangement was also provided for securing the power source electrical conductor adjacent a wellhead to supply power to the downhole electrical conductor by extending into the sealed barrier associated with the wellhead and inhibiting explosions and fires in a hazardous area.
Improvements over the penetrator in U.S. Pat. No. 5,829,882, are described in PCT application WO 94/25726, and related, pending U.S. patent applications, which is a continuation-in-part of U.S. Pat. No. 5,829,882.
While these types of penetrators have proven to be safe and effective, they require a relatively large number of parts and, since the splice between the electrical conductors for the downhole equipment and the power source is located below the wellhead barrier, they require a substantial amount of time to complete.
The problems discussed above were solved by the invention described in pending U.S. Pat. Ser. No. 08/633,244, filed Apr. 16, 1996, entitled "Underground Well Electrical Cable Transition, Seal and Method." That invention dealt with a transition for electrical well cable through the wellhead barrier of an underground well leading to an electrical power cable connected to an above-ground electrical power source, a confined seal for the transition, and a method for forming the transition.
The transition for that invention included a length of electrical well cable extending uninterrupted from an underground well through the wellhead barrier, a connection between the underground well cable and the electrical power cable, the connection being formed outside the wellhead barrier within an area adjacent to the wellhead barrier classified as a hazardous location. The connection is listed and approved for hazardous locations by a nationally recognized testing laboratory ("NRTL") such as, for example, Factory Mutual Research Corporation. A confined seal is located in the well around the electrical well cable for blocking the flow of fluid into or out of the well.
That invention applied to electrical well cable which has an outer protective cable coating and a plurality of insulated electrical conductors projecting from the protective cable coating. A typical electrical well cable includes three electrical conductors, but the invention could be applied to other types of electrical well cable in various shapes, sizes and configurations.
The transition included a primary conduit with an inner surface defining an elongated opening, the primary conduit extending through at least a portion of the wellhead barrier and surrounding a portion of the electrical conductors and a portion of the protective cable coating. An elastomeric seal was provided in the primary conduit for sealing the space between the electrical conductors and the inner surface of the conduit. The elastomeric seal had opposed faces, and a relatively hard backing material located in the primary conduit abutting against both faces of the elastomeric seal. The relatively hard backing material was located around and between the conductors in the inner surface of the conduit. The backing material could also surround at least a part of the protective cable coating that extends into the elongated opening of the primary conduit.
The transition also included an elongated rigid conduit extending between the primary conduit and an opening in the wellhead barrier for each of the conductors. A fluid-tight connection was formed between one end of the elongated conduits and the primary conduit and also between the other end of the elongated conduits and the wellhead barrier openings.
One of the fluid-tight connections included a manifold cap connected to the primary conduit, with openings in the manifold cap for receiving the elongated rigid conduits. A back-up bushing is positioned between the relatively hard backing material and the manifold cap. The backing material was preferably formed of an epoxy putty with good dielectric properties that is resistant to well fluids and which is compressed before it hardens to surround the conductors and fill the spaces in the elongated opening in the primary conduit. The elastomeric seal was preferably formed of synthetic rubber.
A method for forming the confined elastomeric seal included exposing at least one insulated electrical conductor by removing the outer protective coating from a portion of electrical well cable that extends uninterrupted from downhole electrical equipment. A relatively hard backing material, such as the epoxy putty mentioned above, was positioned around the insulated conductor cable and abutting opposing faces of the elastomeric seal. The backing material extended along the insulated electrical conductor on both sides of the seal.
The seal and relatively hard backing material were surrounded along the length of the insulated electrical conductor with a primary conduit for isolating the insulated electrical conductor from the well and forming a seal around the conductor. The seal was then confined between the portions of hardened backing material to prevent well fluids from flowing both into and out of the well between the insulated electrical conductor and the primary conduit.
The elastomeric seal was preferably formed with an outer diameter larger than the opening of the primary conduit, and with openings for receiving the insulated electrical conductors, which are smaller than the outer diameter of the conductors for providing a tight seal between adjacent surfaces. The seal was confined by compressing the epoxy putty before it hardens to fill all the spaces in the primary conduit and around the elastomeric seal, insulated electrical conductor and electrical well cable. A compressing tool connected between the primary conduit and the electrical well cable could be used to compress the epoxy putty and extrude it before it hardens into all of the spaces in the primary conduit.